1) Field of the Invention
The present invention generally relates to image reading apparatuses and, more particularly, to an image reading apparatus reading an image on an original sheet while feeding the original sheet.
2) Description of the Related Art
An image reading apparatus is known in which an original sheet is pressed onto a contact glass or a contact-type image sensor by means of a roller (read roller). For example, Japanese Laid-Open Patent Application No. 5-63925 discloses such an image reading apparatus. In this image reading apparatus, the read roller which presses an original sheet has a width smaller than a width of an original sheet having a minimum size. This is to prevent a projection of opposite ends of the read roller even when a minimum-size original sheet is read.
Since the original sheet is fed only by a rotation of the read roller, an accuracy of a feed speed of the original sheet depends on the read roller. Thus, high accuracy and rigidity are required for the read roller. Accordingly, a shaft of the read roller is made of a metal, and precision machining is required for producing the shaft of the read roller. This causes an increase in a manufacturing cost of the read roller.
Recently, a roller having a shaft formed by plastic molding has been used to reduce the manufacturing cost of the roller. However, it is difficult to achieve high accuracy and rigidity for such a mold-formed shaft, and thus the mold-formed shaft is used only for a roller, such as an eject roller, which does not require high accuracy and rigidity. Additionally, a fiber-reinforced plastic molded shaft may be used for forming the shaft of the read roller instead of the metal shaft.
On the other hand, a plastic molded shaft, which is long and has an appropriate flexibility, has become practically used for the read roller which has a narrow width so that the read roller contacts only a middle portion of the original sheet. This read roller is pressed onto a contact glass or a contact-type image sensor by an elastic force of the plastic molded shaft. This read roller reduces a manufacturing cost since the shaft can be formed by low-cost plastic molding. However, since the shaft of the read roller is flexible, the roller may be displaced in an undesired direction other than the direction toward the contact glass or the contact-type image sensor. Accordingly, there is a problem in that a stable feed of the original sheet cannot be achieved due to an undesired displacement of the roller.
Additionally, when an original sheet is caught between the read roller and the contact glass due to a reason such as paper jamming, the jammed original sheet may be pulled by force. At this time, an excessive force may be applied to the shaft, and thus there is a problem in that a permanent deformation or damage occurs in the shaft.